Electrical apparatus



April 27, 1954 L. l. KNUDSON ELECTRICAL APPARATUS Filed Dec. 5, 1952 wnmiuu,

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Patented Apr. 27, 1954 UNITED STATES PATENT OFFICE ELECTRICAL APPARATUS Lewis I. Knudsen, Norwich, N. Y., assignor to Bendix Aviation Corporation, New York, N. Y., a corporation of Delaware Application December 3, 1952, Serial No. 323,874

4 Claims. 1

This invention relates to electrical apparatus and more particularly to an induction device adapted for use by way of example in apparatus for investigating the operation of the ignition system of an internal combustion engine or the like.

This application is a continuation-in-part of my copending application Serial No. 776,904, filed September 30, 1947.

One of the objects of the present invention is to provide a novel apparatus for magnetically, i. e'., inductively picking up electrical energy from an electrical conductor which means are so constructed as to substantially eliminate the effects of capacity components.

Another object of the invention is to provide novel apparatus of a simplified nature which may be readily associated with an electrical conductor and adapted to respond to changes in the flow of energy through the conductor.

A further object is to provide a novelly constructed radio shielded unit for picking up energy by induction from a single electrical conductor and which may be readily associated with a radio shielded conductor.

Still another object is to provide a novel transformer device which may be readily and quickly inserted in the input lead for an internal electric spark plug or other electrical conductor for generating signals in a circuit which is wholly free of direct electrical connection to said conductor, said signals being in response to voltage variations in said conductor.

The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in conjunction with the accompanying drawing. It is to be expressly undenstood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention, reference for this latter purpose being had primarily to the appended claims.

In the drawings wherein like reference characters refer to like parts throughout the sevv eral views,

Fig. 1 is a side elevational View partly in section and with parts broken away showing one form of device embodying the invention.

Fig. 2 is a detail elevational view with parts broken away and partly in section showing the coil and. core structure of the device shown in Fig. 1 as viewed from the right in said figure; and

Fig. 3 is a section taken substantially on line '33 of Fig. 2.

The single embodiment of the invention illustrated in the drawings, by way of example, is designed for use in conjunction with a radio shielded ignition system of an internal combustion engine but it is to be understood that the invention is not limited to use in such environment. The device as shown comprises a metallic casing 5 which serves as a shield for intercepting electrical and magnetic emanations which would interfere with radio reception and may be fabricated in any suitable manner, and said casing is preferably provided with oppositely disposed outlets or openings 6 and l for the passage of an electric conductor 8 which is preferably insulated as shown. In order that conductor 8 may be conveniently and quickly inserted in a spark plug circuit, for example, of an ignition system, outlet 6 is adapted for connection with a short length of flexible metallic tubing 9 through which cable 8 may extend and terminate in a plug connector (not shown) of the type commonly used for making connection to a shielded spark plug. Outlet i is adapted to threadedly receive a barrel or socket (not shown) of the type found on shielded spark plugs in common use and adapted to receive the terminal of a spark plug lead for connection with the other end of cable 8.

A novelly constructed induction coil unit is mounted within casing 5 in operative relation to cable I; in such a manner that the coil thereof will be energized in response to variations in the flow of current in the cable and so that the current picked up by the coil will be susbtantially free of capacity components. The illustrated coil unit comprises a two-part laminated core Ill-10, the two U-shaped parts of which are secured together in any suitable manner such as by means of a metallic strap l i and a clamp l2 which joins the ends of the strap to form a continuous ring shaped metal core of metallic flux conducting material. The conductor 8 passes through the central opening in core is so that the latter will serve as a path for the lines of magnetic flux created around the conductor by the flow of current therethrough. C'ore ii], it may be fabricated by first wrapping a continuous metal strip around a mandrel having the desired size and thereafter cutting the same into two parts to permit mounting of the coil to be next described. It will be understood, of course, that the core may be fabricated in other known ways and, if desired, the laminations may extend at right angles to those illustrated and consist of fiat rectangular stampings, split for mounting in a pro-wound coil.

A coil 14 has a winding 55 which surrounds a section of one of the U-shaped parts of core 10, the same being tightly wound on an insulating sleeve it and between two insulating end guides 1-H. Said sleeve and guides may be cemented to the core structure or otherwise suitably secured in place thereon. In a suitable embodiment for use in the spark plug circuit of a large aircraft engine, coil winding 15 was constituted by about 1400 turns of No. 38 or No. 40 copper wire. As shown, the ends of winding 15 are connected by means of leads l8 and It to a pair of terminals of a plug and socket connector, only the plug part 20 of which is illustrated as being secured in an opening in the wall of easing ii. If desired, the low potential end of the coil winding may be connected to ground through casing 5. Core H3 is also connected to ground by a lead 2| which is soldered or otherwise suitably secured to the casing at 22.

In order to substantially eliminate the capacity components in the currents inducted in coil 14, a discontinuous metallic sleeve 23, preferably a steel sleeve, surrounds the winding I5. Said sleeve is split at 2d and is connected to ground by a lead 25 which may be an extension of lead 21. A protective covering of tape may also be Wound around the coil and sleeve structure to reinforce the same structurally. Shielding sleeve 23 is effective to pick up the electro-static capacity radiations emanating from conductor 8 and carries the same to ground so that the current induced in winding I5 is substantially free of any capacity components.

The coil unit and cable may be properly positioned and resiliently supported in casing 5 by a yieldable insulating compound 26. The latter is preferably injected into casing 5 under pressure through a small opening 30 while the casing is substantially evacuated so that the entire space within the same will be filled with the compound. The latter may be injected in liquid form and permitted to set to solid form either with or without the application of heat. There are a number of known compounds suitable for this purpose, such as for example, polymerized cashew-nut shell oil. The openings 6 and "I may be closed with suitable covers (not shown) during the filling step and said covers may support a greased rod of suitable size in the place of cable 8, so that when removed a suitable passage will be provided for the cable.

In operation, whenever there is a change in the amount of current fiowing through conductor 8, there will be a corresponding variation in the magnetic flux lines surrounding the conductor and hence passing through coil 44. If the variation is sufficiently rapid and of appreciable magnitude, a how of current will be induced in winding- 15 when the same cut by the magnetic flux lines. When conductor 8 forms a part of a spark plug lead, for example, the circuit including coil 14 is shocked into excitation whenever there is a flow of energy through the conductor causing the spark plug to fire. The signal thus picked up by coil I t may be usefully employed in apparatus for investigating the operation of the entire ignition system of the engine.

The electrostatic shield may, if desired, take a diiferent form from the sleeve 23 around the coil. For example, the shield may be in the form of a metal tube 2'! as illustrated by dotted lines in Fig. 1 and, if desired, sleeve 23 and tube 21 may be used in combination. The enlarged end of tube 2'! is soldered or otherwise suitably secured to the nipple 23 of opening 6 and extends through the central opening of core [0 to a position relatively close to the nipple 29 around opening I. The free end of tube 21 will, of course, be additionally supported and insulated from the casing by the filling compound 25. The shield may also comprise two telescoping tubes, each secured to one of the nipples 28 and 29 in the same manner that tube 2'! is secured. At the telescoping ends, the tubes may have a sufiicient difference in diameters to permit the compound 26 to insulate them from one another. 7

There is thus provided a novel and efficient energy pick-up device which may be suitably designed for ready and quick installation in an electric lead for detecting variations in the flow of current through the lead. Novel means are also provided in the inductive pick-up unit comprehended for eliminating capacity components from the induced energy. The unit is of relatively simple and compact construction and yet sturdy and reliable.

Although only one embodiment of the invention has been illustrated and described in the accompanying drawings and the foregoing specification, it is to be expressly understood that the invention is not so limited. It is not necessary, for example, to provide a complete shielding casing in all. installations. Various other changes may be made particularly in the design and arrangement of the parts illustrated without departing from the spirit and scope of the invention as it will now be understood by those skilled in the art. For a definition of the limits of the invention, reference is had primarily to the appended claims.

What is claimed is:

1. Apparatus of the class described comprising a metallic casing having cable outlets in opposite sides thereof, an electrical conductor supported in the casing and extending between said outlets, a laminated core of magnetic flux conducting metal completely surrounding a section of said conductor in said casing, a metallic tube surrounding said conductor within the core and being secured at only one end thereof to the casing, a coil closely surrounding only a portion of said core and insulated therefrom, a doubleended longitudinally-split metallic sleeve substantially surrounding the periphery of said coil, means electrically connecting said core and sleeve to the casing, an electrical outlet in the wall of said casing having at least one contact electrically connected to the high potential end of said coil, and yieldable electrical insulation completely filling the remaining space in said casing and supporting said coil and core therein.

2. In an induction coil unit, a closed metallic core comprising two U--shaped parts, means including a metallic strap securing said parts toget-her, a coil closely surrounding a section of said core and strap, a double-ended longitudinally-split metallic sleeve extending substantially around the periphery of said coil, a single electrical conductor extending through the central opening in said core, means for grounding said core and sleeve, a casing for the aforementioned elements, a metallic tube surrounding said conductor within the core and insulated therefrom, said tube being secured at only one end to said casing, and a solid yieldable insulating compound filling the space in said casing around said elements and constituting a support for the coil and core in the casing. Y

3. A radio shielded induction coil unit co nprising a closed metallic core, a coil mounted on and surrounding only a portion of said core, a double-ended longitudinally-split metallic sleeve around said coil, a metallic casing surrounding said coil and core, a single conductor supported by and insulated from said casing and extending through the opening in said core, a metallic tube surrounding said cable within the core and in sulated therefrom, said tube being supported at one end by said casing and being otherwise insulated therefrom, means for electrically connecting said sleeve and core to the casing, and a solid mass of yieldable insulation filling the space inside the casing around. said tube, coil and core, said mass constituting the sole support for said coil and core in the casing.

4. Apparatus of the class described comprising a metallic casing having cable outlets in opposite sides thereof, an electrical conductor supported in the casing and extending between said outlets, a laminated core of magnetic flux conducting metal completely surrounding a section of said conductor in said casing, a metallic tube surrounding said conductor within the core and being secured at only one end thereof to the casing, a coil closely surrounding only a portion of said core and insulated therefrom, means electrically connecting said core to the casing, an electrical outlet in the wall of said casing having at least one contact electrically connected to the high potential end of said coil, and yieldable electrical insulation completely filling the remaining space in said casing and supporting said coil and core therein.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,476,121 Smith, Jr July 12, 1949 FOREIGN PATENTS Number Country Date 96,764 Austria Apr. 25, 1924 

